Method of preparing bead-type polymers

ABSTRACT

There is disclosed a method wherein discrete droplets of liquid monomer containing a monomer-soluble free radical-type catalyst are suspended in an aqueous mucilage having plastic flow properties and at least a minimum critical yield value induced by a water-insoluble polymeric thickening dispersing agent such as a carboxyl-form or dual-salt forms of a cross-linked polyacrylic acid. The polymerization is carried out at the usual temperatures under substantially quiescent conditions whereby the droplets are not subjected to sufficient shear to deform or subdivide them. Salts of nitrobenzene sulfonic acids added to the aqueous phase further suppress new particle initiation therein, narrows the particle sized distribution, and produces clearer product suspensions. The products are obtained as permanent suspension of discrete beads usually of spherical shape and having great clarity, low water sensitivity and good electrical properties. The method is ideally adapted to the continuous mode of operation. The suspensions are permanent yet the aqueous phase is easily removed by screening or centrifuging thereby permitting both easy isolation of dry beads and, if desired, easy concentration of the suspension to very high polymer solids levels.

United States Patent [72] Inventor Louis Cohen Avon Lake, Ohio [21]Appl. No. 772,406

[22] Filed Oct. 31,1968

I45] Patented Nov. 16, 1971 [73] Assignee The B. F. Goodrich Company NewYork, N.Y.

{54] METHOD OF PREPARING BEAU-TYPE POLYMERS 12 Claims, No Drawings [56]References Cited UNITED STATES PATENTS 2,108,044 2/1938 Crawford et al.260/17.4 X 2,459,955 1/1949 Morrison et al. 260/17.4 X 2,494,517 1/1950Naps 260/17.4X 2,701,245 2/1955 Lynn 250/895 2,923,692 2/1960Ackermanetal. 3,030,343 4/1962 Jones Primary Examiner-William H. ShortAssistant Examiner-R. J. Koch Attorneys-R. W. Wilson and Harold S. MeyerABSTRACT: There is disclosed a method wherein discrete droplets ofliquid monomer containing a monomer-soluble free radical-type catalystare suspended in an aqueous mucilage having plastic flow properties andat least a minimum critical yield value induced by a water-insolublepolymeric thickening dispersing agent such as a carboxyl-form or dualsalt forms of a cross-linked polyacrylic acid. The polymerization iscarried out at the usual temperatures under substantially quiescentconditions whereby the droplets are not subjected to sufficient shear todeform or subdivide them. Salts of nitrobenzene sulfonic acids added tothe aqueous phase further suppress new particle initiation therein,narrows the particle sized distribution, and produces clearer productsuspensions. The products are obtained as permanent suspension ofdiscrete beads usually of spherical shape and having great clarity, lowwater sensitivity and good electrical properties. The method is ideallyadapted to the continuous mode of operation. The suspensions arepermanent yet the aqueous phase is easily removed by screening orcentrifuging thereby permitting both easy isolation of dry beads and, ifdesired, easy concentration of the suspension to very high polymer 1METHOD OF PREPARING BEAU-TYPE POLYMERS BACKGROUND OF THE lNVENTlON Manyof the commonest monomeric materials, and particularly vinyl chloride,the alkyl acrylates, the alkyl alkacrylates such as methyl methacrylate,and styrene are being polymerized on a very large scale either inaqueous suspension or in aqueous dispersion (i.e. latex form) employingcolloidal suspension agents or soaps and/or synthetic detergent-typedispersing agents. in all of these methods, moderate to vigorousagitation is depended on to suspend and/or disperse, and to maintainsuch suspension or dispersion, during polymerization and to assist heattransfer to reactor cooling surfaces. Such methods, while universallyemployed on a commercial scale for many years are fraught with manydifficulties and are not as economical as might be. For example, in eventhe best of these suspension-type polymerization systems employing amonomer having per se little ability to dissolve its polymer such asvinyl chloride, polymer deposition on the walls of the stirredpolymerization vessel is relatively severe when rated against othercommonly employed solution and emulsion type systems. In the suspensionpolymerization of vinyl chloride it may be necessary to clean thereactor every one or two runs whereas experience with continuoussolution and emulsion polymerization systems of other monomers showsreactor cleaning intervals may stretch for weeks or a month or two ormore. Continuously operating forms of these suspension systems have beenlittle used.

Likewise, Trommsdorf and Schildnecht, in High Polymers, Vol. X, pp. 94through 97, list many other difficulties of the known suspension (orbead or pearl type) polymerization systems. Frequently, and for unknownreasons, agglomeration of the charge can occur, sometimes so rapidly asto lead to destruction of the stirring device, With highly insoluble,tough and hard polymers such as polyvinyl chloride, the failure ofagitation can be nearly catastrophic because of either runawaytemperature and pressure which can be explosive and/or lead to theformation of a solid charge" which can only be removed from the reactorwith the very greatest difficulty and expenditure of large amounts ofhand labor.

The formation of imperfectly formed, adhered, agglomerated, and hollow,cloudy or opaque beads, or even fibrous and colloidal polymercontaminating the beads and therefore necessarily removed byclassification, is also a difficulty.

Such known suspension polymerization systems have employed eitherwater-soluble protective colloids such as gelatin, cellulosederivatives, polyvinyl alcohol, salts of polyacrylic acids, etc., orfinely divided solid mineral-type additives such as bentonite clay assuspension stabilizers. As shown in the above reference, agitation isessential at all times using such additives. Also, such literaturereference shows, p. 74, that the organic polymers serving as suspensionstabilizers be soluble in water but incompletely soluble in the monomerphase.

US. Pat. No. 2,701,245 is the only known instance of a suspensionpolymerization system claiming to employ a quiescent period duringpolymerization. The latter method, however, employs water solublewetting or surface-active agents as an aid in forming monomer dropletsand, as a result, the quiescent reaction medium stratifies, first at thetop and, after polymerization, at the bottom of the reaction vessel.Stratification would likely cause severe reactor fouling in a commercialsize reactor. Even worse, the patent example shows a wastage of fromabout 3 to about 5 percent of the product as a colloidal polymericmaterial which must in some way be separated from the product.

SUMMARY OF THE INVENTION In accordance with the present invention, 1have discovered that the above and other difficulties are avoided by mynew method wherein a liquid monomeric material of low solubility inwater (i.e. a solubility in water below about 5 percent/wt.)

containing a monomer-soluble free radical type catalyst is suspended asdiscrete droplets of a desired size in an aqueous medium thickened witha water-insoluble, highly gelled polymeric suspending/dispersing agentwhich imparts plastic flow properties to such medium and imparts atleast a minimum critical yield value thereto and carrying out thepolymerization under substantially quiescent conditions. The term"substantially quiescent conditions" as thus employed means an absenceof turbulence or the absence of shearing forces sufficient to deform thesuspended droplets of monomer and/or to damage the bead at any stage ofconversion. The reaction medium remains quite mobile (at low shearrates) at all stages of the process and this is so even at solids levelsof 25, 40 percent or more. As a result, such reaction media may bepumped, poured, and/or pressurized through pipe lines or over heatexchange surfaces during the reaction and/or during workup, underconditions wherein the character of flow is not more violent thanplastic or laminar flow.

I have also found that, with monomers that naturally produce stickypolymers, the final reaction medium or polymer suspension will be usefulas a novel pressure-sensitive adhesive. The ability of the process andof the product to reach high solids levels simplifies the preparation ofsuch adhesives. For example, one can prepare directly a suspension atsolids level of 40 to 70 percent/wt. reachable in other systems only byvery careful control and/or by the agglomeration and/or concentration ofmore dilute aqueous latices, but an even simpler procedure is to preparea product of this invention at more moderate solids levels of 25 to 40percent/wt. and to separate therefrom an appropriate portion of theaqueous phase to yield the desired high solids level in the range of 50to 70 percent/wt. or more solids content. The latter operation is, inmost cases, a simple screening or centrifuging operation. The elaborateprocedures of the art to prepare, agglomerate and/or otherwiseconcentrate aqueous latices or emulsions to yield such adhesives is notonly difiicult and expensive but of limited ability to removeelectrolytic and hydrophilic residues present in the original latex.

I have found that plastic flow characteristics in the aqueous media isessential to suspension stability of the order here required and tosuccessful practice of the method of the invention conducted in theabsence of turbulence. Heretofore employed soluable" suspensionstabilizers or colloids such as polyvinyl alcohol, gelatin, cellulosederivatives, soluble polymers such as sodium polyacrylate, and the likeare not capable of imparting plastic flow characteristics, at least ateconomical concentrations. Such known suspension stabilizers evidencenewtonian or pseudoplastic flow behavior. Pseudoplastic flow behavior ischaracterized by an increase in viscosity with decrease in the rate ofshear but at zero shear rates, essentially zero or very low yield value.Thus, known suspension stabilizers merely retard settling and areeffective only in agitated systems. Pseudoplastic or newtonian behaviorof most known thickeners or suspending agents is responsible for theshake well before using" labels on many of our present-day drug,cosmetic and proprietary household formulations since under quiescentconditions the pseudoplastic suspending agent or thickener is of sharplyreduced suspending efficiency.

The water-insoluble suspension stabilizers employed in the method ofthis invention are essentially completely gelled out, when added to anaqueous medium, swell very greatly until the aqueous phase becomes acontinuous, nongrainy gel phase evidencing plastic flow behavior whereinthe medium evidences a minimum critical yield value (or finite shearstress at zero shear rate) sufficient to maintain the monomer dropletsfrozen" in permanent suspension (i.e. no Sedimenta tion orStratification on standing for at least two months). Such media are notunduly viscous at low shear rates encountered in plastic or laminarflow. Many of the reaction mixtures of this invention are no moreviscous at low or moderate shear rates (10 to I00 Sec-l than, forexample, pure glycerinc.

Even though such media do not separate on standing they are easilyseparable into polymer solids and aqueous phase by simple screening,centrifuging or the like.

Reaction rates in this process are normal and subject to the usualcontrol; the molecular weight of the polymer is normal and subject tothe usual control methods; and very high monomer conversions may beachieved without difficulty. Temperature control is no problem, as mightbe expected under nonturbulent conditions, since the reacting mixtureexhibits good plastic flow and may be pressured or otherwise forced toflow in proximity to heat exchange surfaces or through long tubelike orsheetlike (concentric) reactors immersed in or containing a coolingmedium. THe very great suspension stability permits this type ofoperation and, as a result, makes the process an ideal one to carry outin a continuous manner. Also, the very great suspension stabilityreduces polymer buildup on reactor heat exchange surfaces to very lowvalues making it possible to achieve very high onsteam efficiencies foreach reactor.

The method also makes it possible to tailor-make the particle size ofthe product anywhere desired in the range of from about 1 micron orlower to about I centimeter or more in average diameter. The manner inwhich this is accomplished will appear more clearly below.

The product is of the valuable spherical bead or pearl" form with mostmonomers and, with many of the monomers capable of producing opticallyclear polymers, the beads are entirely clear, perfectly spherical,unagglomerated and of a relatively uniform particle size. The watersensitivity and the electrical properties of the polymers are betterthan those achieved in known emulsion and suspension systems. The waterabsorption of a curable copolymer of ethyl acrylate and chloroethylvinyl ether made by the method of this invention, for example, after 4khours in boiling water is only 12.7 percent/wt. increase as compared to138 percent for a similar copolymer prepared in the conventional mannerby coagulation from a latex.

DETAILED DESCRIPTION The amount of the insoluble suspending agent orthickener required in any given circumstance for proper yield value iseasily determined.

The minimum yield value required in the aqueous medium for suspensionstability with any given monomeric material depends on the densitydifference between the monomeric and aqueous phases (labeled DD andexpressed as grams/cm); on the desired or actual radius (R) of thesuspended monomer droplet (expressed in cm.); and, of course, on theacceleration of gravity (g.) expressed in cm./sec. usually 980 cm./sec.The minimum Brookfield Yield Value (BYV) for permanent suspension can becalculated by the formula:

(I) I3YV=[25.6R(D--D,,)g] wherein the terms are as identified above.This equation is valid only for the materials evidencing plastic flowproperties as described in this invention.

In practice one would want to employ aqueous media having a BYV somewhatin excess of the calculated minimum in order to make absolutely certainthat suspension stability is easily achieved and fully maintainedthroughout the reaction. It is preferred to employ aqueous mucilaginousmedia having a measured or actual BYV at least 25 percent and preferablyfrom about 50 percent to 200 percent or more higher than the calculatedminimum.

Actual BYV values conveniently are measured or calculated fromrheological data obtained by the use of the Brookfield RVT Viscometer(operated at the temperature to be utilized in polymerization) wherebyone measures the Brookfield apparent viscosity (in centipoise) at 0.5r.p.m. and again at 1.0 r.p.m. If these data are plotted against shearrate and the curve extrapolated to zero shear rate one obtains BYVdirectly. However, the minimum BYV for permanent stability can beapproximated from the expression:

Approx. B YV Apparent Brookfield Visc. 0.5 r.p.m. Apparent BrookfieldVise. 1.0 r.p.m.

In many cases; a useful and easily measured and calculated viscometricparameter is the ratio (R of the BYV divided by the apparent Brookfieldviscosity measured at 20 r.p.m. This ratio will vary somewhat dependingon the magnitude of BYV. The expression l) given above incorporates anempirical correction factor which compensates for this error. The mediaexhibiting the larger R value will permit the desired suspensionstabilizers with the greatest fluidities.

In general, the BYV values with the preferred suspending agents of thisinvention will be, at a minimum, in the range of 50 to 75 for manycommon monomers and common particle sizes. Most often with many monomersthe practical operating range will be from about 75 to about 250. TheBrookfield apparent viscosity 20 r.p.m. of media of such BYV will be inthe range of about 1 ,000 to about 2,000 cps.

WATER-INSOLUBLE SUSPENDING/DISPERSING AGENTS The suspending agents foundto impart the desired rheology to the aqueous medium in the method ofthis invention are the water, dioxaneand organic solvent-insolublecarboxylic and dual-salt forms or partial dual salts of insolublecarboxylic polymers prepared from a monomeric material selected from theclass consisting of, as essential monomers l) at least one alpha-betaunsaturated carboxylic acid or alpha-beta unsaturated carboxylic acidanhydride and (2) a polyfunctional (i.e. at least two nonconjugatedwherein R is hydrogen or a COOI-I group, and each of R and R is ahydrogen or a monovalent substituent group which is linked to one of thedoubly bonded carbon atoms. Carboxylic acids within this definitioninclude acids such as acrylic acid wherein the double bond is terminalthusly or the dicarboxylic acids such as maleic acid and otheranhydrides of the general structure wherein R and R are monovalentsubstituent groups and especially those selected from the groupconsisting of hydrogen, halogen and cyanogen (-CEN) groups and alkyl,aryl, alkaryl, aralkyl and cycloaliphatic radicals.

Included within the class of carboxylic acids shown in structure (3)above are widely divergent materials as the acrylic acids such asacrylic acid itself, methacrylic acid, ethacrylic acid, alphaandbeta-chloro, bromo, and -cyano acrylic acids, crotonic acid,beta-acryloxy propionic acid, alpha-beta isopropylidene propionic acid,cinnamic acid, maleic acid, fumaric acid, itaconic acid, and manyothers. Polymerizable carboxylic acid anhydrides include any of theanhydrides of the above acids (including mixed anhydrides) ad those ofstructure (5 including maleic anhydride and others. in many cases it ispreferred to copolymerize an anhydride monomer with a comonomer such asmethyl vinyl ether, styrene, and others.

It is much preferred to employ in the method of this invention thepolymeric suspension/dispersing agents derived from polymers produced bythe polymerization of the alpha-beta, monoolefmically unsaturatedcarboxylic acids. Even more preferred are those derived from the acrylicacids and alphasubstituted acrylic acids if the structure:

wherein X is a monovalent substituent selected from the class consistingof hydrogen, halogen, hydroxyl, carboxyl, amide, ester, lactone, lactam,and cyanogen groups.

Most preferred as polymeric suspending/dispersing agents are thoseprepared from the cross-linked interpolymers of acrylic acid itself.These agents are by far the most efficient and have by far the mostdesirable viscosity characteristics, viscosity stability and tremendoussuspending ability.

The cross-linking agents which may be employed with any monomericmixture within the above classes may be any compound, not necessarilymonomeric in nature, containing a plurality (i.e. 2 or more) of terminalpolymerizable monovinylidene CH2=C groups per molecule. illustrative ofthis class of material include polyunsaturated-hydrocarbons,-polyethers, -polyesters, -nitriles, -acids, -acid anhydrides, -ketones,-alcohols and polyunsaturated compounds of this class incorporating oneor more of these and other functional groups. Specifically, there may beutilized divinyl benzene, divinyl naphthalene, low molecular weight(soluble) polymerized dienes such as polybutadiene and other solublehomopolymers of openchain, aliphatic, conjugated dienes (such solublepolymers not containing any appreciable number of conjugated doublebonds) and other polyunsaturated hydrocarbons; polyunsaturated esters,ester-amides and other ester derivatives such as ethylene-glycoldiacrylate, ethylene-glycol dimethacrylate, allyl acrylate,methylene-bisacrylamide, methylene-bismethacrylamide, triacrylyltriazine, hexallyl trimethylene trisulfone and many others;polyunsaturated ethers such as divinyl ether, diallyl ether,dimethyallyl ether, diallyl ethylene glycol ether, diallyl, triallyl andother polyallyl ethers of gylcerol, butene-l,2 diol,l-peneyll,2,3,-propanetriol, the polyallyl, -vinyl, and -crotylpolyethers containing from 2 or 7 or more of these or other alkenylether groupings per molecule and made from polyhydric alcohols such asthe carbohydrate sugars, the so-called sugar alcohols includingerythritol, pentaerythritol, arabitol, iditol, mannitol, sorbital,inositol, raffinose, glucose, sucrose, and many others, and otherpolyhydroxy carbohydrate derivatives, the corresponding polyalkenylsilanes such as the vinyl and allyl silanes; and others. Of this largeclass the polyalkenyl polyethers of the carbohydrate sugars, sugaralcohols and other (polyhydroxy) carbohydrate type derivativescontaining from 2 to 7 alkenyl ether groupings per molecule areparticularly preferred, Such materials are easily prepared by awilliamson type synthesis involving the reaction of an alkenyl halidesuch as allyl chloride, allyl bromide, methallyl chloride, crotylchloride and the like with a strongly alkaline solution of one or moreof the polyhydroxy carbohydrate derivatives. Cross-linking agents ofthis class produce essentially completely gelled, cross-linkedcarboxylic polymers which (I) retain their rheological efficiency duringneutralization and during service, (2) have the ability to swell mosthighly and (3) produce smooth, creamy and nongrainy mucilaginouscompositions of the greatest suspendingefficiency.

As indicated above, the insoluble polymeric suspending/dispersing agentis lightly cross-linked so as to remain highly swellable in water. Aslittle as 0.05 to 0.l percent/wt, more preferably 0.1 to 6 percent/wt.and most preferably O.l to 4 percent/wt. (all based on the total weightof monomers) of the cross-linking monomers produce such highly swellablepolymers. With the preferred carbohydrate ether type crosslinkingmonomers of high functionality, smaller proportions from about 0.2 toabout 2.5 percent/wt. of the latter are sufficient to obtain the desiredpolymer.

As little as 0.02 to 0.05 percent/wt. (based on the weight of mucilage)of the suspending/dispersing agents of this type are capable ofimparting the desired yield values for permanent suspension. One may, ifdesired, employ from about 0.05 to 2 percent/wt. of such agents. Morepreferable is from about 0.05 to about 0.50 percent/wt. of the agent.Such small proportions indicate the very great suspending efficiency ofthese agents.

Products obtained by neutralizing or partially neutralizing the carboxylcontent of the suspending agent with only ordinary monovalent alkalissuch as sodium hydroxide, potassium hydroxide, ammonia and the like areseriously deficient in their ability to assist in breaking-up ordispersing the liquid monomer into droplet form. The acid-form ofunneutralized polymer has this ability and so do the alkali/aminefdual-salts of the same polymer. The acid-form polymer, however, is muchless efficient than the dual-salts and must be employed in higherconcentrations. Such dual-salts are prepared employing two or moreneutralizing agents including at least one neutralizer from each of thefollowing two classes:

A. Monovalent alkaline materials including ammonia and the alkali metalhydroxides, oxides, carbonates, and the like: and

B. Basic organic long chain amines containing at least six carbon atoms,more preferably between about l0 and about 30 carbon atoms, permolecule.

in general, the polymeric suspending/dispersing agents swell most highlyin water at a pH of from about 5 to about 8 and this range is a good onefor good polymerization rates with many common monomers. This desired pHrange is obtained by neutralizing from about 15 to about mol percent,more preferably from about 20 to about 40 mol percent of the carboxylcontent present in the acid-form agent. The amine-salt groupings on thepolymeric agent are believed to improve its association with the monomerand thereby assist the breaking up or dispersion of the monomer indroplet form. in this sense, the acid-form and alkali/amine dual saltforms of the agents are both thickeners and polymericsuspending/dispersing agents whereas the single alkali salts are merethickeners.

The class A neutralizing agents useful in this invention includeammonia, sodium hydroxide, sodium oxide, sodium carbonate, sodiumbicarbonate, potassium hydroxide, potassium oxide, potassium carbonate,potassium bicarbonate, the hydroxides, oxides, carbonates, andbicarbonates of lithium, rubidium and cesium, and others.

The class B basic organic amines useful in this invention include thelong chain aliphatic primary, secondary and tertiary amines andquaternary amines, and alkylene oxide treated amines of this type,containing from six to 30 carbon atoms or more. More preferred are theamines containing from 10 to 30 or more carbon atoms. Most preferred arethe ethylene oxide condensates of the latter class of long chain amines.Specific examples of these long amines which may be utilized includen-hexyl amine, n-octyl amine, tri-n-octyl amine, n-decyl amine,di-n-decyl amine, n-dodecyl amine, di-n-dodecyl amine, stearyl amine,ethylene oxide/dodecylamine condensates, and tetraalkyl ammoniumhydroxides such as tetraoctyl ammonium hydroxide and tetradodecylammonium hydroxides. The preferred amines are the dodecyl amines and theamine/ ethylene oxide condensates of the formula;

wherein n is a number between about 10 and about and x y equals about15. Such compounds may have molecular weights in the range of betweenabout 750 and about 1,500 and, for this reason, not a very high molarproportion need be utilized to effect a very noticeable increase in theorganophilicity of the polymeric suspending/dispersion agent.

In fact, only about 0.2 to about 10 mol percent of the carboxyl contentof the suspending/dispersing agent need be reacted with a long chainamine, more preferably from about 0.5 to about 2.5 mol percent willusually be sufficient. Expressed in terms of weight ratios suchproportions with respect to the class A" neutralizer will range fromabout 0.01 to 0.02:1 to about 0.2:1.

With many monomers it is necessary, usually, to include in the mucilagea suppressor or inhibitor of aqueous phase polymerization. In some casesit is the small but finite solubility of the monomer in water wherebymonomer transfers to the aqueous phase as fast as it is polymerizedtherein. In the latter, cases, a very substantial proportion of thetotal monomer may be consumed in this manner. In the usual case, polymerformed in the aqueous phase is of a very fine powdery nature mostdifficult to recover without loss and the presence of which undulycomplicates bead recovery operations and leading to high polymer losses.In some cases, even monomers of low solubility in water produce suchresults without the aqueous phase inhibitor present. In the latter casessome obscure transfer reaction may be transferring monomer from thedroplets to polymer nuclei in the aqueous phase at a rate above thatindicated by the solubility of the monomer in water. Since chanceimpurities in water and the other ingredients may encourage or increasesuch reactions, the addition of a small amount of an inhibitor to theaqueous phase insures bead-only formation. Polymerization in the aqueousphase manifests itself by a milky appearance in the suspension andsometimes by a frosty or milky appearance of the beads. With theinhibitor, both the suspension and the beads remain clear throughout thereaction.

I have found that alkali and ammonium salts of nitrobenzene sulfonicacids are soluble in the mucilage and are remarkably efficient as thistype of inhibitor. Other watersoluble inhibitors of free radicalcatalysts and chain-terminating type compounds may be utilized. Thesalts of 2,4- dinitrobenzene sulfonic acid are particularly effective.Only very small proportions of these inhibitors are required sinceexcellent results are obtained at concentrations of from about 50 toabout 250 ppm.

Such agents are strongly ionic and tend to reduce the mucilageviscosity. When used, a small increase in the concentration of thelatter from about 5 percent to about 25 percent may be required toachieve the desired rheology. The mucilage is easily prepared bycombining the dry polymeric agent, neutralizers and inhibitors, if any,and gently agitating until the mixture appears smooth and creamy.Alternatively, all ingredients of the polymerization reaction mixtureincluding the long chain amine but not the alkali may be combined andgently agitated until the mucilage forms but without monomer dispersion.As a last step a dilute solution of alkali is added and agitationcontinued. Almost immediately the reaction mixture thickens and theseparate liquid monomer phase disappears as the droplets appear.

The separately prepared aqueous mucilaginous composition and the liquidmonomer containing catalyst may be combined and intermixed under theappropriate conditions of shear in order to cause the breaking up of thecontinuous monomer phase into droplets of the desired size. If themonomer is volatile, this operation is best carried out in a closedvessel, with or without an inert atmosphere or a vacuum over the mixingliquids. A completely filled vessel approach may be utilized. Oncedispersed or suspended, however, the suspension shows unique and quiteunexpected properties. For example, a reaction medium of this inventioncontaining a suspension of 10 percent/wt. concentration of vinylchloride containing isopropyl percarbonate catalyst can be placed in anopen beaker and polymerization carried out under quiescent conditions atroom temperature without boiling being observed. This unusual result isobtained at a temperature about 38 C. above the normal boiling point ofvinyl chloride. Thus, the aqueous mucilaginous medium of this inventionappears capable, in some cases at least, of completely suppressingnucleation of boiling of a volatile monomer. This could be one propertyof the medium which can aid in maintaining the beads free of voids andalso can aid in suppressing polymer buildup on reactor surfaces.

The mixture of mucilage and monomer is agitated with the intensity ofagitation selected or varied to yield the desired monomer droplet size.Droplet size is inversely related to shear rate during this operation.With any given combination of monomer and mucilage, the requisite degreeof agitation for a given droplet size needs be determined experimentallyby trial-and-error but this is not difficult due to the pronouncedtendency of an organic liquid of ordinary viscosity to break up intodroplets in such a medium. One can obtain a rough measure of therequired intensity of agitation by placing the correct or desiredproportions of mucilage and monomer in a stoppered test tube and countthe number of inversions of the test tube required to suspend themonomer in the mucilage. With many of the common monomers and withmucilages having at least the minimum critical yield value required, amere 30 or 40 inversions of the test tube at the rate of 30 inversionsper minute will produce suspensions of relatively large droplets (l to 3mm. dia.). Finer droplet sizes can be achieved with many common mixingdevices and/or homogenizer-type equipment. In large scale, repetitivecommercial operations procedures for obtaining the desired droplet sizecan be prepared in terms of the mixer or agitator type, agitation rate,agitation time and temperature.

The monomer so suspended must contain a small amount of a monomeroroil-soluble catalyst such as is described below. Such monomer may alsocontain, if desired, certain other additives such as molecular weightcontrollers including the long chain aliphatic mercaptans employed inthe polymerization of acrylic rubbers. Catalysts such as the alkanoyl,aroyl, alkaroyl and aralkanoyl diperoxides and monohydroperoxides, azocompounds, peroxy-esters, percarbonates, and many other free radicaltype catalysts may be employed with the monounsaturated monomers.Illustrative peroxides which may be employed include benzoyl diperoxide,lauryl diperoxide, diacetyl peroxide, cumene hydroperoxides, methylethyl ketone peroxide, diisopropylbenzene hydroperoxide,2,4-dichlorobenzoyl peroxide, napthoyl peroxide, t-butyl perbenzoate,di-t-butyl perphthalate, isopropyl percarbonate and many others.Illustrative azo-type catalysts include azo-bis-isobutyronitrile alpha,alpha'-azodiisobutyrate, and many others. The choice of any particularfree radical catalyst is dictated partially by the choice of monomericmaterial, by color requirements of the polymer, and to some extent bythe temperature of polymerization to be employed.

POLYMERIZATION The polymerization step may be carried out at anytemperature normal for the monomeric material to be polymerized. Ingeneral, the range between about 0 C. and about 150 C. will polymerizemost known monounsaturated monomeric materials, A more preferred rangeis between about 25 C. and about C.

In order to facilitate temperature control under the relativelyquiescent conditions of the method of this invention, the reactionmedium is brought into contact with cooling surfaces cooled by water,brine, evaporation, etc. In general, the polymerization reactor for themethod of this invention should have a considerably higher ratio ofsurface to volume than is employed in agitated systems. A preferred typeof reactor is one or more long, narrow tubes immersed in a cooling baththrough which the reaction medium is forced to flow at moderate speeds.Such tubes can be arranged in coils, banks (as in steam boilers) orlayers to secure the required reaction volume. Such tubes can vary fromabout 0.5 inch to I or 2 inches or more in diameter depending on thescale of operations. Another type of reactor is a reaction chamber muchlonger than its width in which are placed cooled plates or fins.

MONOM ERIC MATERIALS POLYMERIZED It is a unique feature of the processof this invention that the monomeric material to be polymerized islimited only by the requirement for solubility of less than about 5percent/wt. in water and by the availability of an operablemonomer-soluble free radical catalyst capable of mass-polymerizing themonomer in question. Monomers which polymerize normally to form stickypolymers are easily employed in the process with no difficulty due tothe very great suspending efficiency of the aqueous medium. Theso-called critical period" in many older suspension polymerizationsystems, wherein the partially polymerized monomer droplets pass throughasticky condition at an intermediate conversion, is not observed. Infact, sticky, viscous monomer/polymer syrups sometimes referred to asprepolymers may be dispersed and suspended in the thickened aqueousmedium and the polymerization of the monomer content of the dropletscompleted. The latter facility can be made use of in the preparation ofhigh-impact resins wherein a rubbery impact improver or plasticizer maybe dissolved in the monounsaturated monomer prior to suspension in theaqueous medium,

Illustrative monounsaturated monomers which may be employed in themethod and products of this invention include vinyl chloride, vinylbromide, vinyl fluoride, fluoride, vinylidene chloride,tetrafluoroethylene, styrene and nuclear-substituted styrenes, the alkylacrylates, the alkyl alkacrylates such as methyl methacrylate,acrylonitrile, ethyl vinyl ,benzene, vinyl naphthalene, and many othersas well as mixtures of any two or more of these and/or with still othersimilar monomers. In some cases, very minor proportions (i.e. up to l or2 percent/wt.) of the more water-soluble monomers such as vinyl acetate,acrylic amides, acrylic acids, and others may be added to the moreinsoluble monomers and the polymerization conducted in a thickenedaqueous medium containing an aqueous phase polymerization suppressantsuch as the salts of nitrobenzene sulfonic acids. Likewise, smallproportions (i.e. up to about 5 percent/wt.) of polyunsaturated monomerssuch as divinyl benzene, glycol diacrylates, etc., may etc., employedprovided the catalyst employed is capable of effecting the masspolymerization of the monomer mixture.

The preferred monomeric materials are vinyl chloride; the alkylacrylates such as ethyl acrylate, butyl acrylate 2-ethylhexyl acrylateand others, and mixtures of these or with still other monomers such as2-chloroethyl vinyl ether; the alkyl alkacrylates such as methylmethacrylate; styrene and nuclearly substituted halostyrenes; andacrylonitrile.

PRESSURE-SENSITIVE ADHESIVES As indicated above, the method of thisinvention is easily applied to produce superior/pressure-sensitiveadhesives in the novel form of bead suspensions. Such adhesives comprise(I) a high solids (50 percent --70 percent or more by weight)suspension/dispersion of a lightly cross-linked polymer of a higheralkyl acrylate and (2) a tackifler. Such a product contains beads of asticky polyacrylate and such bead-form is retained, due to the lightcross-linking, even after the suspension is coated on a substrate andheated to effect drying and formation of an adhesive deposit. Suchbead-form adhesive deposit, when properly compounded with tackifiers,stabilizers, etc., evidences very high and tenaciously retained peelstrength. Such an adhesive is admirably suited to application to paperand plastic substrates in the preparation of pressuresensrtive tapes.

As indicated such adhesive products are produced from monomeric mixturespredominating (i.e. more than 50 percent/wt.) in the higher alkylacrylates, that is, alkyl acrylates in which the alkyl group containsfrom four to eight carbon atoms both with and without other comonomerssuch as acrylonitrile, methyl methacrylate, styrene and others togetherwith a very small amount ofa cross-linking monomer such as anyhereinabove described employed in producing the suspending/dispersingagent but preferably a glycol diacrylate or other polyacrylate polyesterof a polyhydroxy compound containing from three to five or six acrylategroups per molecule. The presence of a third comonomer often produces anadhesive of greater strength. Only from about 0.005 to about 0.20percent/wt. of the cross-linking monomer based on the total weight ofmonomers, more preferably about 0.005 to about 0.05 percent/wt, need beutilized. The object here is to impart integrity to the beads but not toimpair their ability to cohere one to another and to adhere to thesubstrate when applied as an adhesive layer.

As indicated, the bead-type pressure sensitive adhesive for mulation ispreferably compounded with a tackifier such as rosin, low molecularweight polystyrene (molecular weight below about 3,500), low molecularweight polyvinyl acetate, and the like. Rosin is the best and leastexpensive tackifier but imparts an undesirable yellowish cast to theadhesive layer. Polystyrene and polyvinyl acetate in the adhesiveformulation produce clear, colorless adhesive deposits. From about I0percent to about 40 percent/wt. of a tackifler or tackifiers willusually be sufficient in most pressure-sensitive adhesive formulations.

The invention will now be described in still greater detail withreference to-several specific examples which are intended asillustrative only and not as limiting the scope of the invention.

EXAMPLE I CONTINUOUS POLYMERIZATION In this example, a mixture ofparts/wt. of ethyl acrylate and 5 parts/wt. of 2-chlorethyl vinyl etheris prepared and stored in a closed water-cooled container under an inertatmosphere of nitrogen. To this mixture there is added 0.2 percent/wt.of benzoyl peroxide and 0.02 percent/wt. of dodecyl mercaptan. Themixture is agitated briefly and the temperature maintained at or nearroom temperature to insure against premature mass polymerization.

In another vessel there are admixed demineralized water and 0.07percent/wt. based on the water of Carbopol 94I (registered trademark ofThe B. F. Goodrich Company; product is the carboxylic form of acopolymer of the monomeric mixtures described containing anhydrousacrylic acid and a mixture of polyallyl ethers of sucrose containing anaverage of from aboutthree to about six allyl ether groups permolecule). The mixture is stirred gently for about 1 hour after whichaqueous sodium hydroxide and a long-chain amine Ethomeen C-25 made byArmour and believed to be a reac tion product of ethylene oxide and along-chain aliphatic amine containing about 25 carbon atoms) are addedto form a partial dual-salt form of the copolymer in which about 25 molpercent of its total carboxyl content is neutralized by the caustic andabout 0.5 mol percent by the amine. Also added to this mucilage are -l45p.p.m. of the sodium salt of 2,4- dinitro-benzene sulfonic acid. Themixture is agitated gently until smooth. The BYV value of the resultingsmooth, nongrainy mucilage is 154 and its apparent Brookfield viscosityat 20 r.p.m. is 2,010 cps.

all"

The contents of the two vessels are combined in a weight ratio of 25percent/wt. of the monomer and 75 percent/wt. of the mucilage. Themonomer phase is slowly added to the water phase while rapidly agitatingthe latter with a employed contains 0.20 percent/wt. of the carboxylicform Carbopol 941 in demineralized water. The BYV of the latter i584:its Brookfield apparent viscosity rpm. is 1,060 cps;

and its pH is 3.3. The monomer concentration is either per- Lightninmixer forming a uniform suspension of droplets 5 cent/wt. or percent/wt.0.36 mm. in average diameter. The resulting suspension is The mucilageis prepared by adding the suspendtransferred to a pressure vessel underan atmosphere of ing/dispersing agent to water and very gently agitatingfor a nitrogen. The suspension is then pressured with nitrogen and fewminutes until a stable viscosity and smooth nongrainy apcaused to flowthrough a tubelike reactor immersed in a water pearance is reached. Themucilage and the monomeric bath maintained at the indicatedtemperatures. Such reactor 10 material are combined in a small sealedreaction vessel which consists of 88 ft. of i k-inch (i.D.) stainlesssteel tubing is placed in a rack which rotates at about 30 rpm. suchthat fabricated into a double coil l5-inches high and l5-inches in thevessel is tumbled end-over-end. Only about 1 minute is diameter. Thetotal internal volume of such tubelike reactor is required to form astable suspension of large (1 to 3 mm. dia.) about 1 gallon, aconvenient size which facilitates acquisition 5 monomer droplets in theaqueous phase. The sealed reaction of flow rate data. Variousexperiments are conducted, see vessels are then purged with nitrogen,sealed again and table I below, wherein the flow rates and residencetimes in mounted immovably in a constant temperature water bath thereactor are varied. The product is every case are small maintained at 60C. Following polymerization the vessels are pearllike or beadlikeparticles of a rubbery terpolymer in opened and the product worked upeither by pouring the mixwhich the chlorethyl vinyl ether groupsfunction as reactive 20 ture onto a 70 mesh Tyler scale) screen and thenwashed with groups in vulcanization. Such polymer is similar to that ofU.S. ,water on the screen or the beads suspended in water and sub- Pat.No. 2,568,659. The data below show a range of jected to several slurrytype wash operations carried out under equivalent conditions which canpertain to reactions as just agitation and decanting off the wash waterafter each cycle. described, n A m The products are dried in a vacuumoven at 60 C. or 100 C.

Bath Prestemper- Approxsure Output ature, Mean imate drop, Residencetime in rate. C. velocity, shear rate lbs./ coil-min. gaL/hr. requiredft./sec. (sec. NRO ft?" Bath temperature required to reach 95%conversion in residence time indicated.

curve 01' the muciln ge. *Caleulated.

value of 138 percent for a similar polymer prepared in the conventionalmanner by coagulation of a latex.

in the above experiments the suspension of polymer leaving the tubelikereactor is run directly onto a screen. The collected polymer spheres arewashed several times with clear water and dried at C. in a vacuum ovenwhere the particles coalesce forming directly sheets of rubbery product.The

aqueous mucilaginous medium is reusable and can be recycled 1 to theprocess in whole or in part after any necessary readjustment of itsviscosity characteristics.

EXAMPLE ii in this example, an unneutralized mucilage of Carbopol 94l"is employed in the batchwise copolymerization of several differentcombinations of methyl acrylate, ethyl acrylate and n-butyl acrylateboth with and without acrylonitrile and in one case with chloroethylvinyl ether. The mucilage The data are as follows, in which proportionsare parts/wt.

Sample Number 11 15 16 34 33 Monomer phase:

Butyl ecrylate 88 88 95 20 95 Ethyl acrylate... Methyl ecry1ate Acrynitrile Z-chloroethyl viny Benzoyl peroxide 2 0. 032 0. 010 Porophor-N"Expressed as parts/wt. per 100 parts/wt. of total monomer.""Porophor-N", made by Du Pont said to be azo-bis-butyronitrile.

Sample Number 11 15 16 34 33 Percent monomers 25 40 25 25 25 Reactlntime hours... 16 16 16 16 2 Percent yield 93 93 97 84 Polymerdescription Bead average diameter, mm 2 2 1. 5 2 2 Inherent viscosity(0.4% in DMF at .5

1 Very soft clear beads. 14 Soft white beads.

The dried polymeric products have the properties expected and, inaddition, have very low sensitivity to water and very good color.

EXAMPLE [I] To compare the use of an unneutralized against a neutralizedmucilage, mixtures of 95 parts/wt. of ethyl acrylate and parts/wt. of2-chloroethyl vinyl ether are polymerized in a Carbopol 941 mucilageneutralized as in example I. It is found because of losses and it isexpected that the actual conversions are somewhat higher than indicatedabove.

EXAMPLE lV that the concentration of the suspending agent in theneutral- 5 ized mucilagc must be reduced to 0.05 t00.07 percent/wt. toThe procedure of example lll lS twice duplicated with a obtain similarrheological properties. Several other variations small-scale batch and alarge scale batch, but both employing are employed including the use ofa mercaptan molecular a monomeric mixture and temperature similar tothat of exwcight controller, several catalysts, and a nitrobenzenesulperiment l29. The size of the monomeric droplets are mea fonic acidsalt. The data are as follows: sured as are those of the beads ofpolymer obtained. The data Sample No 26 41 118 124 129 Monomer phase:

Ethyl acrylate, part/wt 95 95 95 2, CLEVE, parts/wt 5 5 5 Benzoylperoxide, PHR... 0. 4 0.2 0. 2 Thiophenol l Dodecyl mercaptan 0. 02Aqueous phase:

0.05% suspending agent X X 0.07% suspending agent. X X X Percent/wt.monomer.. 24 25 25 25 25 BYV (aqueous phase).. 150 150 102 102 102Brookfield app. viscosity at 20 rpm 1,950 1, 950 1, 375 1, 375 1, 375 pH(aq. phase) 5. 2 5.2 6.4 5.4 5.4 Percent total neutralization. 20% AllPercent ehtorneen neutralized... 1. 2 0. 15 0. 15 O. 15 0. 15Polymerization:

(a) Temp. C 28 60 80 (b) Time,hrs 17 s4 is 1.5 1.5 (c) Conversion,percent/wt 86 93 92 94 Polymer suspension:

Appearance Cloudy Cloudy 2 Clear 2 Clear 2 Clear Average bead diameter,mm. 0. 5 3 1. 5 2. 0 2. 0 B ad appearance... (4) (a) a) a (a) Inherentviscosity 7 4. 64 2. 26 2. 76 2. 47 1. 47 Percent gel 4. 6 0.5 5.8 0 0 l2-chloroethyl vinyl ether.

1 Experiments118,124and sulionic acid in aqueous phase.

Fused.

* Frosty white.

5 Frosty clear.

5 Crystal clear.

7 As in Example II.

Several observations on the above data are worthwhile. First,

note the lowered concentration of suspending agent and reducedBrookfield Viscosity with the neutralized suspensions as against theunneutralized suspension of example II (0.05

percent or 0.07 percent/wt. vs. 0.20 percent in example 11). Second notethat the final suspension of polymer from examples 26 and 41 is cloudywhereas those of the remaining ex- ,periments which employed aninhibitor of aqueous phase polymerization are clear. At the same timenote that the beads from a cloudy suspension are frosty and/or opaquewhereas both the suspension and the beads in the experiments employingan inhibitor of aqueous phase polymerization are clcar. Lastly, note thewide range of polymerization times and temperatures and also in themolecular weight of the polymer ob-, tained. These variables producedtheir usual and expected effeet. Note the significant molecular weightreduction (lowered [.V. values) in experiment 129 where a small amountof mercaptan is dissolved in the monomer. Data such as these are thesource of the earlier statement herein that the polymerization in thismethod is subject to normal control. It is clear that with a monomersuch as ethyl acrylate and CLEVE, soluble in water to the extent ofabout 5 percent/wt., it is ordinarily preferred to employ an agent forsuppression of aqueous phase polymerization.

In the experiments, work up of the polymer in experiments 26 and 41 isdifficult by simple screening so the suspension is diluted 4 or 5 timesits original volume with water to cause the. polymer beads to settle outafter which the cloudy liquid content is decanted off. Polymer fines arelost by this operation. 1 Several water washes are applied in the samemanner after; which the rubbery polymer is dried in an oven for 2 hourso0" In the remaining experiments the clear suspension of headsis merelypoured into ii o0-mesh screen (Tyler Scale washed several times withfresh water on the screen, and finally dried in a vacuum oven for 16hours at room temperature. The yields are somewhat low, especially inexperiments 26 and 4i,

129 employed 145 p.p.m. of the sodium salt of 2,4-dinitrobenzene are asfollows:

Percent Droplet Bead wt.

slightly in conversion to polymer. The viscosity of thc suspension isstill high after completion of the reaction.

A portion of the unpolymerized monomer-in-mucilage suspension preparedin example IV is mixed for 2 minutes in a small laboratory bench sizeWaring blender with volts applied to its motor. This high shear mixingresulted in a stable, white (opaque), small particle size dispersion.The suspension is polymerized as in example Ill and IV and worked up bythe decantation technique described above. The comparative 5 results areas follows:

Example lV (large) Example lV (fine) Wt.Ave. Particle Size-Microns 3303.4 Dried Polymer Crystal Particles l'uscd lo- Clear together intocontinuous mass due to work-up procedure. Slighll) cloudy.

This simple experiment indicates the very wide range in particle sizeobtainable simply by varying the amount of shear employed in making thesuspension. This experiment shows that high shear mixing sharply reducedthe particle size of already suspended large droplets.

EXAMPLE V In this example, styrene is converted to clear spherical beadsof a moderately large size easily visible to the naked eye. Mucilage Aand a monomer/catalyst/modifier solution B are combined, the vesselpurged with nitrogen and then 2.55 ml. of 0.1 N NaOH are added and thesmall reaction vessel hand shaken to effect dispersion of the monomer.The styrene droplets are plainly visible to the naked eye and thedispersion is clear. The materials employed are:

0.2%}wt. "Carbopol 941 mucilage 49 ml. Ethomeen C-25" 1.1 ml. Water 100grams Distilled Styrene 70 ml. Benzoyl Peroxide 0.268 gram Dimethylaniline solution (1) 0.100 gram (1) in Heptane The vessel and thesuspension are allowed to stand in an air oven maintained at 60 C. overa weekend. When examined the suspension is still clear indicating verylittle, if any, polymerization had occurred in the aqueous phase. Thiswould be as expected due to the very low solubility of styrene in water.The beads of polymer are isolated by screening and are washed on thescreen with fresh water and dried in a vacuum oven for 2 hours at 80 C.There is thus recovered a total of 53 grams of polystyrene beads whichare perfectly clear and of expected properties.

EXAMPLE V1 agent containing200 p.p.m. of 2,4-dinitrobenzene sulfonicacid) is placed in a tubelike reactor and 0.150 ml. of a 0.1 percent/wt.solution of Ethomeen C-25 added and 3.75 grams of liquid (polymerizationgrade) vinyl chloride monomer added. There are then added in rapid order1.31 grams of a solution in vinyl chloride (35 parts by wt. per 100part/wt. of

vinyl chloride) of Santicizer 160 (Monsanto, a polyvinyl chlorideplasticizer; sp. Gr. 1.118, refractive index at 25 1.53-1.54), 0.075gram (2 parts/wt. per 100 parts/wt. of monomer) of Epoxol 9-5 stabilizer(Swift; an epoxidized fatty acid ester) and 0.015 grams of benzoylperoxide (0.4 part/wt. per 100 parts/wt. of monomer). A small portion ofthe vinyl chloride is allowed to boil off and purge the oxygen over themixture before the tube is sealed. At this point there appeared to belittle tendency for the monomer to disperse when the tube is inverted anumber of times. At this time 0.238 ml.

of 0.1N NaOH solution is injected by a hypodermic syringe quietly in a60 C. oil bath and observed. In about one hour the a small amount ofunreacted vinyl chloride escapes. When the mixture is stirred with aspatula, however, the remainder of the unreacted vinyl chloride boilsoff. The reaction mixture is very clear at this point indicating littleor no polymerization in the aqueous phase. The contents of the reactorare poured through a SO-mesh (Tyler scale) screen, washed and dried forone-half hour at 45 C. in a vacuum oven. Approximately 3.1 grams ofplasticized polyvinyl chloride beads are recovered which consist ofabout 1.72 grams of polymer and about 1.38 grams of plasticizer andEpoxol stabilizer (a total of parts/wt. per parts/wt. of resin). Inspite of this very high plasticizer level there is no agglomeration ofthe beads or sticking thereof to the reaction vessel duringpolymerization.

Polyvinyl chloride beads made in a manner similar to this and having anaverage bead size of about 5 microns when added as a diluent resin to aplastisol formulation substantially reduce the viscosity of theplastisol. The beads of polyvinyl chloride are translucent rather thanclear, and are perfect spheres due, apparently, to shrinkage andinsolubility of the polymeric phase in the monomeric phase. In spite ofthis, the method produces directly a product of very considerablecommercial utility and obtainable, at this time, in no other way.

EXAMPLE Vll In this example, a slightly cross-linked polymer of2-ethylhexyl acrylate is prepared by the method of this invention foruse as a pressure-sensitive adhesive. The materials utilized are:

Mucilage A Monomer Sol. B

mucilage-IZO grams 240 grams Water"'240 grams Benzoyl pcroxide0.24

gram

0.1% Aq. Ethomeen C-25- Sulfole B8"""0.041l

18 grams gram 0.1N NaOH 6 ml.

" Demineralized Contains 0.01%lwt. of an unknown cross-linking monomerbut which could he a glycol diacrylate T. M. Phillips-t-dodecylmercaptan 'fii'rhtiii e is made $255555 the water to a conven tionalpolymerization reactor having a variable-speed stirrer capable of speedup to 350 r.p.m.; next the dry Carbopol" is added and the mixtureallowed to agitate r.p.m.) until the Carbopol is thoroughly swollen;next the long chain amine Ethomeen C-25 is added and the stirringcontinued for about 5 minutes; and lastly the NaOH is added and thestirrer speed increased to 200 r.p.m. At this point, the MonomerSolution 8" is added by pouring it into the liquid vortex in the reactorwhile agitating at 160 to 300 r.p.m. The resulting mixture is thenpassed once through a motor-driven homogenizer and then back into thereactor to reduce the monomer droplet size. The stirrer is then shut offand hot water (80 C.) admitted to the reactor water jacket. A sampletaken after 45 minutes of reaction showed a conversion of 98.5 percent.The reaction is allowed to stand for a total of 1 hour and 45 minutes toensure completion of reaction and low odor. The product at this point isa smooth suspension of 37.7 percent/wt. of very small beads difficult tosee without magnification.

The latter product is concentrated by passing once through a centrifugeto produce a final product containing 69 percent/wt. of polymer beads.The clear liquid obtained from the centrifuge has a viscosity similarbut slightly lower than that of the original mucilage. To theconcentrated suspension of beads there is added 20 percent/wt. based onthe bead weight of a rosin tackifier emulsion. A thin layer of theresulting composition is spread on a substrate and heated in a vacuumoven to dry. A similar coating is prepared from a similar formulationprepared in a similar manner but without cross-linking. When the twoadhesives are photographed through a microscope the deposit ofcross-linked beads shows a surface in which numerous spheres of polymerare present whereas the deposit prepared from the polymer having nocross-linking has flowed during drying to a smooth surfaced deposit. Thebead-type deposit of cross-linked polymer shows several times higherpeel strength than the smooth-surfaced control deposit. The photographof the bead-type deposit is remarkably similar in appearance to asimilar photograph of the freshly prepared suspension of liquid monomer.In a series of experiments in which the degree of cross-linking isvaried a definite maxima in peel strength at very low cross-linkinglevels equivalent to about 0.01 percent/wt. of cross-linking monomer isobserved.

lclaim:

1. In a method of polymerizing a monounsaturated monomer containing adissolved monomer-soluble free radical catalyst in aqueous suspension toform bead-type polymer, the improvement which comprises utilizing assaid monomer a monomeric material soluble in water not to exceed aboutpercent/wt. and containing not more than about 5 percent/wt. ofpolyunsaturated monomer, mixing from about percent to about 40 percentof said monomeric material with from about 90 percent to about 60percent of an aqueous mucilaginous composition having plastic flowproperties whereby said composition evidences a minimum yield valuesufficient to permanently suspend said monomer as droplets between about1 micron and about 1 centimeter in average diameter, and carrying outpolymerization of said droplets suspended in said mucilaginouscomposition at a temperature of about 0 C. to about 150 C. and in theabsence of shearing forces exerted thereon thereby to produce beads of aresinous polymer substantially spherical in shape, said mucilaginouscomposition containing from about 0.05 to about 0.5 percent/wt. basedon; the weight of said mucilaginous composition of a water-insoluble,highly swellable polymeric suspending/dispersing agent in the acid formor the dual-salt form of an essentially completely gelled, lightlycross-linked carboxylic polymer prepared from l) at least one alpha-betaunsaturated carboxylic acid or alpha-beta unsaturated carboxylic acidanhydride and from 0.05 to 6 percent/wt. based on the total weight ofsaid carboxylic polymer of (2) a cross-linking monomer containing atleast two nonconjugated W MN groups per molecule, provided that whensaid agent is of said acid form sufficient of its carboxyl groups areneutralized to induce in said composition a pH between about 5 to about8, said neutralization being effected mainly by a monovalent alkalinematerial and from about 0.5 to about 2.5 mol percent of said carboxylgroups by a basic organic amine containing at least six carbon atoms permolecule, and said minimum yield value is given by the expression[25.6R(D-Do) g.] wherein R is the radius of said suspended droplets,D-Do is the difference in density between the aqueous and monomericphases, and g. is the acceleration of gravity.

2. The method as defined in claim 1 and further characterized in thatsaid aqueous mucilaginous composition contains, as an additionalingredient, from about 50 to about 250 p.p.m. based on the weight ofmucilaginous composition of an alkali or ammonium salt of a nitrobenzenesulfonic acid as an inhibitor of aqueous phase polymerization and theproportion of said polymeric suspending/dispersing agent is increasedfrom about 5 to percent to compensate for any ionic effect ofsaidadditional ingredient.

3. The method as defined in claim 1 and further characterized by saidpolymeric suspending/dispersing agent being a cross-linked interpolymcrof (i) a carboxylic monomer selected from the class consisting of thealpha-beta unsaturated carboxylic acids and anhydrides and (ii) fromabout 0.

to 6 percent/wt. based on the total weight of monomers of across-linking monomer containing at least two nonconjugated CH groupsper molecule.

4. A method as defined in claim 3 and further characterized by saidaqueous mucilaginous composition having a yield value from about 25percent to about 200 percent higher than said calculated minimum value.

5. The method as defined in claim 1 and further characterized by saidmonounsaturated monomer being selected from the class consisting of thevinyl halides, styrene and nuclearly-substituted helostyrenes, alkylacrylates, alkyl alkacrylates, acrylic nitriles, and mixtures thereofand said polymeric suspension/dispersion agent is derived from a water,dioxane-, and organic solvent-insoluble copolymer of an acrylic acid andan alkenyl polyether of a polyhydroxy carbohydrate derivative containingfrom two to about six alkenyl ether groupings per molecule.

6. The method as defined in claim 5, and further characterized by saidpolymerization being conducted at a temperature regulated in the rangeof from about 0 to about 150 C. while said suspension is being movedunder plastic flow in contact with heat exchange surfaces.

7. The method as defined in claim 5 and further characterized in thatsaid aqueous mucilaginous composition contains from about 50 to about250 p.p.m. based on the weight of mucilaginous composition of awater-soluble alkali or am monium salt of a nitrobenzene sulfonic acidas an inhibitor of aqueous phase polymerization, said polymerizationbeing conducted at a temperature regulated in the range of from about 25to about C. while said suspension of droplets is being moved underplastic flow in contact with heat exchange surfaces, and said beads ofpolymer are recovered by passing the said suspension of beads through ascreen adapted to retain said beads.

8. The method as defined by claim 1, and further characterized by saidmonomeric material being a mixture of an alkyl acrylate and achloroethyl vinyl ether, by said aqueous mucilaginous compositioncontaining from about 50 to about 250 p.p.m. based on the weightofmucilaginous composition of the sodium salt of 2.4-dinitrobenzenesulfonic acid as an inhibitor of aqueous phase polymerization, by saidpolymerization being conducted at a temperature of from about 25 toabout 100 C. while said suspension of droplets is being moved underplastic flow in proximity to heat exchange surfaces, and said beads arerecovered by passing the said suspension of beads through a screen sizedto retain said beads.

9. The method as defined in claim 1, and further characterized by saidmonounsaturated monomer being styrene.

10. The method as defined in claim 1 and further characterized by saidmonounsaturated monomer being vinyl chloride.

11. In a method of preparing stable aqueous suspensions of polymericmaterials wherein the polymeric materials constitute more than about 50percent/wt. of the total suspension, the improvement which comprisespolymerizing under plastic flow conditions at a temperature of about 0.C. to about C. and a solution of a monomer-soluble peroxygen catalyst ina monounsaturated monomer selected from the class consisting of vinylhalides, styrene and nuclearly-substituted halostyrenes, alkylacrylates, alkyl alkacrylates, acrylonitrile and mixtures thereof whilesuspended as discrete substantially spherical droplets of such monomerfrom about 1 micron to about 1 centimeter in average diameter in anaqueous mucilaginous composition containing from about 50 to about 250p.p.m. based on the weight of mucilaginous composition of an alkali orammonium salt of a nitrobenzene sullonic acid as an inhibitor of aqueousphase polymerization and possessing plastic flow properties including aBrookfield yield value at least 25 percent higher than is calculatedfrom the expression [25.6R (D--D,,)] wherein R is the average radius ofsaid monomer droplets, D D is the difference between the densities ofthe aqueous and monomer phases, and g is the acceleration due togravity, there being employed from about 10 percent to about 40percent/wt. of said monomer and from about 90 percent to about 60percent/wt. of said aqueous mucilaginous composition thereby producingan aqueous suspension of said polymeric material in the form ofsubstantially spherical beads of average size ranging from about 1micron to l centimeter, and thereafter removing that proportion of saidaqueous mucilaginous composition from the said reaction mixture as isrequired to concentrate it and produce a final product containing morethan about 50 percent of its total weight as said beads, said aqueousmucilaginous composition deriving its rheological characteristics byreason of containing from about 0.05 to about 0.50 percent/wt. based onthe weight of said mucilaginous composition of a lightly cross linked,highly swellable interpolymer of acrylic acid with from about 0.2percent to about 2.5 percent/wt. based on the total monomers of saidinterpolymer of a polyalkenyl polyether of a polyhydroxy carbohydratederivative containing from 2 to about 6 alkenyl ether groupings permolecule said interpolymer being neutralized to a pH of between about 5and 8 mainly by a monovalent alkaline material and from about 0.5 toabout 2.5 mol percent of the carboxyl groups by a basic organic aminecontaining at least six carbon atoms per molecule.

@2 3? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION patent3,620,988 Dated November 16, 1971 Inventor(s) LOUIS COHEN It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

r- Col. 2, line 6 4 "out" should read --and--.

Col. 3, line 13, "THe" should read --The-. Col. 4, line 1 "stabilizers"should read --stabilities--;

line 21, after "viscosity" insert --at--. Col. 5, line 10 "ad" shouldread --a.nd--; line 20, "if" should read --of--. Col. 10, line *(ldelete before "l -i5".

Col. 12, space betv'a'een "is" and "8min line 3; same line 3 after"viscosity" insert at--; line 20 after "mesh" insert line 63 "reacln"should read --reaction--.

Col. 13, in the example after "2,CLEVE, parts/wt." insert ----(1 line 72after "hours" insert --at--.

Col. 1 in Example IV in headings after "Droplet wt.average particlesize" insert ----(1 Col. 16, line 17, after "are second occurrence,insert -not--.

Signed and sealed this 15th day of August 1972.

(SEAL) Attest:

EDWARD M. FLETCHER, JR- RGBERT GOTTSCHALK Attesting Officer Commissionerof Patents

2. The method as defined in claim 1 and further characterized in thatsaid aqueous mucilaginous composition contains, as an additionalingredient, from about 50 to about 250 p.p.m. based on the weight ofmucilaginous composition of an alkali or ammonium salt of a nitrobenzenesulfonic acid as an inhibitor of aqueous phase polymerization and theproportion of said polymeric suspending/dispersing agent is increasedfrom about 5 to 25 percent to compensate for any ionic effect of saidadditional ingredient.
 3. The method as defined in claim 1 and furthercharacterized by said polymeric suspending/dispersing agent being across-linked interpolymer of (i) a carboxylic monomer selected from theclass consisting of the alpha-beta unsaturated carboxylic acids andanhydrides and (ii) from about 0.1 to 6 percent/wt. based on the totalWeight of monomers of a cross-linking monomer containing at least twononconjugated CH2 groups per molecule.
 4. A method as defined in claim 3and further characterized by said aqueous mucilaginous compositionhaving a yield value from about 25 percent to about 200 percent higherthan said calculated minimum value.
 5. The method as defined in claim 1and further characterized by said monounsaturated monomer being selectedfrom the class consisting of the vinyl halides, styrene andnuclearly-substituted helostyrenes, alkyl acrylates, alkyl alkacrylates,acrylic nitriles, and mixtures thereof and said polymericsuspension/dispersion agent is derived from a water-, dioxane-, andorganic solvent-insoluble copolymer of an acrylic acid and an alkenylpolyether of a polyhydroxy carbohydrate derivative containing from twoto about six alkenyl ether groupings per molecule.
 6. The method asdefined in claim 5, and further characterized by said polymerizationbeing conducted at a temperature regulated in the range of from about 0*to about 150* C. while said suspension is being moved under plastic flowin contact with heat exchange surfaces.
 7. The method as defined inclaim 5 and further characterized in that said aqueous mucilaginouscomposition contains from about 50 to about 250 p.p.m. based on theweight of mucilaginous composition of a water-soluble alkali or ammoniumsalt of a nitrobenzene sulfonic acid as an inhibitor of aqueous phasepolymerization, said polymerization being conducted at a temperatureregulated in the range of from about 25* to about 100* C. while saidsuspension of droplets is being moved under plastic flow in contact withheat exchange surfaces, and said beads of polymer are recovered bypassing the said suspension of beads through a screen adapted to retainsaid beads.
 8. The method as defined by claim 1, and furthercharacterized by said monomeric material being a mixture of an alkylacrylate and a chloroethyl vinyl ether, by said aqueous mucilaginouscomposition containing from about 50 to about 250 p.p.m. based on theweight of mucilaginous composition of the sodium salt of2.4-dinitrobenzene sulfonic acid as an inhibitor of aqueous phasepolymerization, by said polymerization being conducted at a temperatureof from about 25* to about 100* C. while said suspension of droplets isbeing moved under plastic flow in proximity to heat exchange surfaces,and said beads are recovered by passing the said suspension of beadsthrough a screen sized to retain said beads.
 9. The method as defined inclaim 1, and further characterized by said monounsaturated monomer beingstyrene.
 10. The method as defined in claim 1 and further characterizedby said monounsaturated monomer being vinyl chloride.
 11. In a method ofpreparing stable aqueous suspensions of polymeric materials wherein thepolymeric materials constitute more than about 50 percent/wt. of thetotal suspension, the improvement which comprises polymerizing underplastic flow conditions at a temperature of about 0* C. to about 150* C.and a solution of a monomer-soluble peroxygen catalyst in amonounsaturated monomer selected from the class consisting of vinylhalides, styrene and nuclearly-substituted halostyrenes, alkylacrylates, alkyl alkacrylates, acrylonitrile and mixtures thereof whilesuspended as discrete substantially spherical droplets of such monomerfrom about 1 micron to about 1 centimeter in average diameter in anaqueous mucilaginous composition containing from about 50 to about 250p.p.m. based on the weight of mucilaginous composition of an alkali orammonium salt of a nitrobenzene sulfonic acid as an inhibitor of aqueousphase polymerization and possessing plastic flow properties including aBrookfield yield value at least 25 percent higher than is calculatedfrom the expRession (25.6R (D- Do))2/3 wherein R is the average radiusof said monomer droplets, D - Do is the difference between the densitiesof the aqueous and monomer phases, and g is the acceleration due togravity, there being employed from about 10 percent to about 40percent/wt. of said monomer and from about 90 percent to about 60percent/wt. of said aqueous mucilaginous composition thereby producingan aqueous suspension of said polymeric material in the form ofsubstantially spherical beads of average size ranging from about 1micron to 1 centimeter, and thereafter removing that proportion of saidaqueous mucilaginous composition from the said reaction mixture as isrequired to concentrate it and produce a final product containing morethan about 50 percent of its total weight as said beads, said aqueousmucilaginous composition deriving its rheological characteristics byreason of containing from about 0.05 to about 0.50 percent/wt. based onthe weight of said mucilaginous composition of a lightly cross linked,highly swellable interpolymer of acrylic acid with from about 0.2percent to about 2.5 percent/wt. based on the total monomers of saidinterpolymer of a polyalkenyl polyether of a polyhydroxy carbohydratederivative containing from 2 to about 6 alkenyl ether groupings permolecule said interpolymer being neutralized to a pH of between about 5and 8 mainly by a monovalent alkaline material and from about 0.5 toabout 2.5 mol percent of the carboxyl groups by a basic organic aminecontaining at least six carbon atoms per molecule.
 12. The method asdefined in claim 11, and further characterized in that saidmonounsaturated monomer comprises an alkyl acrylate in which the alkylgroup contains from four to eight carbon atoms and from about 0.005 toabout 0.20 percent/wt. based on the total weight of monomers of across-linking monomer, and said reaction mixture is concentrated tocontain more than about 60 percent/wt. of the resulting lightlycross-linked beads.